Radio frequency coil



July 7, 1931. A. E. ,B AUMANN 1,813,137

RADIO FREQUENCY COIL Filed Nov. 25, 1925 FIG. 1

WITNESSES ATTORNEY Patented July 7, 1931 UNITED STATES PATENT OFFICE RADIO FREQUENCY COIL Application filed November 25, 1925.

The invention relates to radiofrequency coils and more particularly to shielding and coupling means for such coils.

An object of the invention is to provide a novel form of shielding means to screen a radio receiving inductor from the influence of powerful radio frequency fields, thereby improving selectivity-in a receiving circuit embodying such inductor.

Another object of the invention is to ut1- lize such shielding means as a coupling means to an input or collector circuit.

A further object of the invention is to utilize such shielding means as a control for oscillation in a receiving circuit.

The invention further consists in the several features hereinafter set forth and more particularly defined by the annexed claims.

In the accompanying drawings, Fig. 1 is a diagrammatic view of a radio receiving circuit including the shielded coil of the present invention;

Fig. 2 is a longitudinal sectional view through a coil embodying the invention; and

Fig. 8 is a transverse sectional view thereof taken on the line 33 of Fig. 2.

In these drawings, 10 indicates a hollow supporting form of suitable insulating material, such as hard rubber, upon which is wound a coil 11 preferably disposed in spaced coil sections 12 and 13. If desired,

the supporting form 10 may be of skeletal character in order to minimize di-electric losses, or in some instances the coil may be of self-supporting character. In the present case, the ends of the coil are connected to ter minal posts 14 and 15, respectively, which are preferably disposed at opposite ends of the supporting form 10.

The coil sections 12 and 13 are surrounded by annular metal shields 16 and 17, respectively, each carrying a temrinal post 18. The shields are preferably slightly spaced from the winding and are each provided with a gap 19 in order to minimize eddy currents.

With these provisions, the high frequency resistance of the coil is not unduly increased.

In the present instance, each shielding band is provided with inturned flanges 20 at opposite edges to bear on the supporting form Serial No. 71,379.

10, but in some cases the shield may be supported upon the winding, if interposed insulation is provided. The coil sections are preferably disposed in adjacent inductive relation as shown, but it is not essential that they occupy this relation.

In the diagram of Fig. 1, the coil forms part of an ultra-audion receiving circuit including a threeelement thermionic detector tube 21, the coil being tuned by a variable condenser 22. As is well known, this circuit provides automatic regeneration but is somewhat unstable because of a marked tendency towards oscillation. It is found, however, that the shielding means of the invention serves to stabilize the circuit by reason of the presence of such means in the radio-frequency field of the coil. The coil may, of course, be used in various other types of circuits.

The shield 16 is connected by its binding post 18 to' an antenna 23 while the shield 17 is connected to a ground 2a. The collector circuit thus comprised may also include tuning elements, such as a variable inductor 25. However, the inductor 25 may be omitted. in some instances. IVith the above-de-- scribed connections the shields form coupling elements by which the coil is electrostatically coupled to an input circuit, such as the collector circuit shown in the diagram. Under adverse conditions the shield 16 may surround a relatively small part of the total coil winding, and in some instances the entire coil may be surrounded by a single shield.

The present invention accordingly provides a shielding means for improving selectivity by minimizing or eliminating local pick-up incident to the collector characteristic of an exposed coil, and affords means for coupling the coil into another circuit and for controlling the tendency towards oscillation in certain types of receiving circuits.

lVhat I claim as new and desire to secure by Letters Patent is:

1. The combination with a solenoidal radio-frequency coil and a tubular supporting form therefor, of a discontinuous anlie nular metallic shielding band surrounding said coil and having inturned flanges at opposite edges beyond the ends of the coil resting on said tubular supporting form.

2. The combination of a radiofrequency coil having spaced solenoidal coil sections, and annular metallic shielding members each surrounding a coil section and being Wider than said coil section and both annular members forming coupling elements for said coil sections.

3. The combination of a solenoidal radio- 'frequency coil forming part of a receiver input circuit, and a pair of discontinuous annular metallic shielding bands surrounding different sections of said coil and each being Wider than its co-operative coil sec tion, one of said annular bands forming an antenna coupling element for transferring signal energy to said input circuit and the other band forming a ground coupling element.

4;. The combination of a solenoidal radiofrequency coil forming a part of a receiver input circuit, and an annular metallic band surrounding said coil out of electrical contact therewith and having its adjacent ends out of contact, said metallic band lying adjacent the coil to form an electrostatic coupling element for transferring radio-frequency signal energy to said coil and being Wider than the coil to form a shielding element.

5. The combination with a tunable re generative radio-frequency receiving cir cuit, of an inductor in said circuit, and a metallic shielding band surrounding said inductor and forming a means for preventing oscillation in said circuit and for transferring signal energy to said inductor.

In testimony whereof, I aflix my signature.

ALFRED E. BAUMANN. 

